Heterozygous Runx2 mutant mice also display all the representative features of CCD, including open fontanelles and hypoplastic clavicles, but not the dental anomalies because mice only have one set of teeth with no replacement dentition (Selby et al., 1993; Komori et al., 1997; Otto et al., 1997). This evidence concerns the gene RUNX2 and cleidocranial dysplasia 1.